Method of producing multiple-wall composite pipes

Abstract

An outer pipe is diametrically expanded by heating and an inner pipe is diametrically contracted by cooling with a coolant introduced into the inner pipe to produce between the pipes a clearance just sufficient for insertion of the inner pipe into the outer pipe, and then the coolant is pressurized to expand the inner pipe against and together with the outer pipe, the pressure being removed after the pipes have expanded to a specific diameter of the joint therebetween. The tightness of the fit between the pipes due to the expansion is further increased by the subsequent thermal shrinkage of the outer pipe and thermal expansion of the inner pipe.

We claim: 
     
       1. A method of producing a multiple walled composite metal pipe, said pipe being formed of an outer pipe and an inner pipe inserted therein, said respective pipes being initially disposed in radially spaced apart relationship to establish a clearance therebetween, including the steps of: (a) heating said outer pipe to an average temperature in excess of that of said inner pipe to establish a temperature differential between the pipes, while maintaining said clearance which causes a small coefficient of heat transfer between the pipes, to thermally expand the outer pipe thereby to increase the clearance;   (b) introducing fluid pressure into said interior surfaces of said inner pipe and urging said inner pipe to plastically expand into contact with said outer pipe with a designated temperature differential; and   (c) decreasing the temperature of said outer pipe to cause contraction of the same and decreasing said fluid pressure applied to said inner pipe for urging the inner pipe into compression, permitting each of said pipes to be joined into a composite pipe with a tight fit.   
     
     
       2. A method of producing multiple walled composite pipe according to claim 1, in which the temperature differential is imparted and the clearance is increased by additionally cooling the inner pipe. 
     
     
       3. A method of producing multiple walled composite pipe according to claim 1, in which the fluid pressure is applied by a liquid medium introduced into the inner pipe and pressurized. 
     
     
       4. A method of producing multiple walled composite pipe according to claim 2, in which the fluid pressure is applied by a cold liquid medium introduced into the inner pipe and pressurized to thereby function doubly as a coolant for cooling the inner pipe and as a pressure applying medium. 
     
     
       5. A method of producing multiple walled composite pipe according to claim 3, in which the liquid medium is water. 
     
     
       6. A method of producing multiple walled composite pipe according to claim 4, in which the cold liquid medium is cold water. 
     
     
       7. A method of producing a multiple walled composite metal pipe, including the steps of: (a) providing separately an outer pipe and an inner pipe which are to be joined together;   (b) heating the outer pipe to an average temperature in excess of that of said inner pipe to establish a temperature differential between the pipes;   (c) disposing the inner pipe into the outer pipe while maintaining said temperature differential and also maintaining a clearance which causes a small coefficient of heat transfer between the pipes;   (d) introducing fluid pressure into said interior surfaces of said inner pipe and urging said inner pipe to plastically expand into contact with said outer pipe with a designated temperature differential; and   (e) decreasing the temperature of said outer pipe to cause contraction of the same and decreasing said fluid pressure applied to said inner pipe for urging the inner pipe into compression, thereby permitting each of said pipes to be joined into a composite pipe with a tight fit.   
     
     
       8. A method of producing a multiple walled composite pipe according to claim 7, in which the temperature differential is imparted by additionally cooling the inner pipe.